Research On Acoustic Wave Prediction Method Of Fracture-cavity Carbonate Formation Physical Parameters

In the influent of the development of the multi-scale pore and fracture,in the process of exploration and development in carbonate oil and gas resources,generally,it is difficult to accurate 1y evaluate the reservoir and face the trouble of wellbore instability and collapse.It is important to base on rock mechanical parameters for optimizing parameters of drilling and completion and reconstructing reservoir and designing other engineering,and orosity is one of the important parameters of reservoir evaluation.It is so different to accurate evaluation of carbonate rock porosity,mechanical strength and other physical parameters that the problems are still big issues for carbonate reservoir pore structure is complex and strong heterogeneity that is different from the homogeneous formation.On the basis of the domestic and foreign literature research,for the carbonate rock in the holes,small size of fractured reservoir,through a large number of numerical simulation experiment on the porosity carbonate rock,rock mechanics parameters,fracture toughness and different frequency wave transit time and attenuation coefficient of relationship,establish the prediction method based on acoustic properties of rock mechanics parameters and porosity.The main achievements are as follows:(1)Under the condition of numerical simulation,the correlation between porosity and sonic transit time is poor,and the sonic transit time can not reflect the change of porosity.(2)There is a good correlation between porosity and attenuation coefficient and when the change of pore radius,there is a big effect of relationship between porosity and coefficient of attenuation,the more information as below:radius distribution in 1.6 mm to 1.8 mm,the logarithmic function law must be obeyed between porosity and P250KHz attenuation coefficient;the exponential function law must be obeyed between porosity and P250KHz attenuation coefficient when radius distribution in 1.0mm to 1.6 mm.(3)Considering the influence of pore size,the porosity prediction model of carbonate rock based on the acoustic attenuation coefficient is established.(4)Under the condition of numerical simulation,botih P250KHz interval transit time or P50KHz interval transit time and elastic modulus correlations are relatively poor,are not suitable for used to predict the elastic modulus;the relationship between acoustic attenuation coefficient and the elastic modulus showed a good linear negative correlation,and the aperture,seam inclination,stitch density on the P50KHz attenuation coefficient and elastic modulus of smaller;selected as a predictor variable attenuation coefficient,establishes a prediction equation of elastic modulus.In the analysis condation,the correlation interval transit time between elastic modulus,Poisson's ratio,compressive strength and is poor,and the interval transit time can not be used in the prediction of rock mechanical parameters.In the analysis condation,rock mechanics parameters and acoustic wave attenuation coefficient has good correlation,such as elastic modulus,compressive strength and acoustic attenuation coefficient of a linear negative correlation;Poisson than with the acoustic attenuation coefficient of a linear positive correlation.(5)In the analysis condation,there is a big influent of the natural crack size,pore size for fracture toughness,the overall performance is as below:with the increase of crack length and reduce the fracture toughness;with the increase of the pore size and with the increase of the scale of natural fracture and variation of pore size on gradually decreasing fracture toughness;there is a better linear correlation between fracture toughness and acoustic attenuation coefficient.